1. Field of the Invention
This invention relates to a hepatic parenchymal cell growth factor obtained by the recombinant DNA technology; to a gene encoding it; to a transformant carrying an expression vector which comprises at least a promoter sequence required for the expression of a protein, a sequence encoding a signal peptide, a DNA sequence encoding human hepatic parenchymal cell growth factor, and a terminator sequence; and to a process for the production of human hepatic parenchymal cell growth factor by culturing the transformant.
2. Description of the Prior Art
The liver is the most highly differentiated and largest adenogenous organ in a living body. It exhibits various important functions such as treatment (metabolism), storage, detoxication, decomposition, excretion and the like of various nutritive substances (carbohydrates, proteins, lipids, vitamins, hormones and the like), and especially it plays an important role in the intermediate metabolism of a living body.
These functions are sustained by hepatic parenchymal cells which are controlled by various hormones in a living body and may show remarkably active proliferation in certain cases. In a rat, for example, it has been known that even after surgical resection of about two-thirds of the liver the remaining hepatic tissue promptly grows and may be restored to its original size in about 10 days. On the other hand, patients suffering from hepatic carcinoma have been treated by partial hepatectomy followed by regeneration.
A large number of researches and investigations have been pursued to elucidate the mechanism of hepatic regeneration by the proliferation of hepatic parenchymal cells, with reports suggesting the presence of hepatic parenchymal cell growth factor. Especially, some of the present inventors found that plasma from patients with fulminant hepatitis had a markedly high activity to proliferate hepatic parenchymal cells (Biomed. Res., 6, 231 (1985) and Exp. Cell Res., 166, 139 (1986)) and succeeded for the first time in the world in purifying the proliferation-activating factor as a single protein (Japanese Patent Application Kokai No. 22526/1988 and J. Clin. Invest., 81, 414 (1988)).
This human hepatic parenchymal cell growth factor (human hepatocyte growth factor; to be referred to as "hHGF" hereinafter) had a molecular weight of approximately 76,000 to 92,000 as estimated by SDS-PAGE under non-reducing conditions, but SDS-PAGE under reducing conditions revealed two bands at molecular weights of 56,000 to 65,000 and 32,000 to 35,000. Nakamura et al. reported rat platelet derived factor having similar activity (Biochem. Biophys. Res. Commun., 122, 1450 (1984)), and estimated its molecular weight to be approximately 27,000 by SDS-PAGE (Proc. Natl. Acad. Sci. USA, 83, 6489 (1986)). Thereafter, they purified the factor as a homogeneous protein and reported that the purified factor was a protein having a molecular weight of 82,000, which consisted of two polypeptides having molecular weights of 69,000 and 34,000 (FEBS Letters, 224, 311 (1987)).
Except for the above mentioned hHGF and rat HGF, there has been no report on any hepatocyte growth factor which has been purified as a homogeneous protein. Even with regard to the hHGF and rat HGF, we know of no report concerning their primary structures and corresponding cDNA base sequences.
A large amount of hHGF will be required when an examination is to be performed in order to elucidate the function of hHGF in a living body in detail and/or its effects on the hepatic regeneration in a patient with hepatopathy. However, isolation and purification of a large amount of hHGF from plasma of patients with fulminant hepatitis are not so easy in view of labor, time and economy, and stable isolation of only hHGF from sera in which various infectious agents exist is extremely difficult to achieve. Because of these reasons, stable and large scale isolation and purification of hHGF from plasma of patients with fulminant hepatitis have not been attempted.